FIGS. 3 and 5 show a prior art sheet metal pulley A in which a circular base part and a peripheral wall for winding a belt are integrally formed by working, or the like, a flat sheet metal blank.
The sheet metal pulley A of FIG. 3 has a recess part 11 for accommodating a bearing (not shown), in an inner peripheral portion of a circular base part 1. A cylindrical peripheral wall 2 having poly-V grooves 21 and an ear 22 is integrally formed in the outer peripheral end of the base part 1. The base part 1 has a flat annular part 12 surrounding the recess part 11. The ear 22 has a double layer structure consisting of a first inclined part 23 which extends from the annular part 12 on the side of the base part 1, and a second inclined part 24 which is folded toward one face of the first inclined part 23 so as to overlap with the first inclined part.
In the sheet metal pulley A of FIG. 5, an ear 22 is formed so as to have a single layer structure, and the end part of the peripheral wall 2 on the side of the ear 22 is integrally connected with the base part 1.
In the sheet metal pulley A of FIG. 3, when a poly-V belt (not shown) is wound around the peripheral wall 2 and the pulley A is then operated, a crack a which is directed from the inner side to the outer side may be formed in a relatively short period in a folded portion 25 in the vicinity of the boundary of the first inclined part 23 and the second inclined part 24 as shown in FIG. 4. Also in the sheet metal pulley A of FIG. 5, a crack a which is directed from the inner side to the outer side may be formed in a relatively short period in a connecting portion 26 between the end part of the peripheral wall 2 on the side of the ear 22 and the base part 1.
The formation of the crack a and its cause in the sheet metal pulley A has intensively been investigated. As a result, it is found that, when the pulley is operated, the peripheral wall 2 around which a belt is wound, vibrates or oscillates about the folded portion 25 or the connecting portion 26 functioning as the fulcrum, with the result that the folded portion 25 or the connecting portion 26 is excessively fatigued.
The present invention is a result of studying the above-mentioned circumstances. It is, therefore, an object of the present invention to provide a sheet metal pulley in which a crack is hardly formed, by improving the structure of a base part connected with an end part of a peripheral wall so that, even when the peripheral wall vibrates or oscillates as the pulley is operated, fatigue is prevented from excessively occurring in one position.